STUDY OF ENVIRONMENTAL RADIOACTIVITY IN PALESTINEBY IN SITU GAMMA-RAY SPECTROSCOPYAdnan Lahham1,*, Hussein Al-Masri1 and Adnan Judeh21Center for Radiation Science and Technology, Al-Quds University, PO Box 20002, Jerusalem, Palestine2Department of Environmental Radiation, Palestine Environmental Quality Authority, Ramallah, Palestine

Received November 13 2008, revised April 26 2009, accepted April 27 2009

This work presents qualitative and quantitative evaluation of environmental radioactivity in the central and southern areas ofthe West Bank, Palestine. For this purpose, the technology of in situ gamma-ray spectroscopy is used with a scintillation of7.6 3 7.6 cm NaI(Tl) crystal connected to multichannel analyzer InSpector 2000 from Canberra instruments and laptop com-puter. Gamma-ray spectra were collected using the detector placed 1 m above the ground surface. Calibration of the detectionsystem for in situ measurements of gamma-emitting radionuclides in open terrain is performed theoretically using MonteCarlo techniques. Measurements are conducted in 18 locations in 3 regions across the West Bank. The vast majority ofidentified radionuclides are naturally occurring gamma-emitting sources (the decay products of 238U, 232Th and 40K). Theonly identified anthropogenic radionuclide is 137Cs. Activity concentrations of 40K, 238U, 232Th as well as the total outdoorgamma dose rate from these radionuclides were determined from the gamma-ray spectra. The highest activity concentrationsof the three primordial radionuclides were 203 Bq kg21 for 40K, 32 Bq kg21 for 238U and 30 Bq kg21 for 232Th. The totaloutdoor gamma dose rate calculated for the whole study area at 1 m above ground ranged from 6 to 30 nGy h21 with a meanof 18+++++7 nGy h21, which represents about 30% of the world average value.

INTRODUCTION

Radioactivity is a permanent part of our environ-ment, and has been since the creation of the Earth.Sources of radioactivity can be put in two generalcategories: naturally occurring and man made. Thenatural radiation sources that the humans are beingexposed to include many components that can varysignificantly with space and time(1). Externalexposures from environmental radioactivity arisefrom gamma rays produced by some of the primor-dial radionuclides. The main contributors to thegamma dose rate are 208Tl and 228Ac from 232Thdecay chain and 214Pb and 214Bi from 238U decaychain in the top 30 cm of soil(2).

Knowledge of radiation levels in a country fromvarious radioactive sources is considered as an attri-bute of qualified protection from the harmful effectsof ionising radiation and as a part of informing thepublic about the state of their environment. Theassessment of concentrations of radionuclides depos-ited in environmental components can also providevaluable information of general scientific character,e.g. about the principles of elements and compoundsmigration in various media. Every locality in theenvironment is characterised not only by its ownexposure rates, but also by its spectrum, which mayvary significantly from case to case. The variation ofthe spectrum is due to various representations of

main natural radionuclides (K, U and Th) in differ-ent locations. This spectrum also varies with positionabove sea level, under the ground, above water areas,etc. This change in the spectrum of a given naturalradiation field results in various responses of energy-dependent detectors. Therefore, it is necessary todetermine exactly the spectral characteristics of thegiven location. The best measurement method inthis case is the in situ gamma-ray spectrometry, e.g.the direct measurement of radioactivity in openterrain. This study is the first of its kind in Palestineand aims at providing information about the levelsof naturally occurring and possible contaminationby man-made radioactivity in the Palestinianenvironment.

STUDY AREA

In situ gamma-ray spectroscopy measurements wereconducted in selected areas of the central andsouthern parts of the West Bank; particularly inJerusalem, Bethlehem and Hebron districts. Figure 1shows the locations of in situ field measurements.Most of the investigated sites are located inJerusalem area where the main campus of Al-QudsUniversity is situated. Bethlehem and Hebrondistricts are located in the southern part of theWest Bank, 8 and 36 km south of Jerusalem,respectively(3).

The geology of the study area consists of the fol-lowing formations: Abu Dies formation (Jerusalem

*Corresponding author: lahham@crst.alquds.edu,lahham@science.alquds.edu

# The Author 2009. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Radiation Protection Dosimetry (2009), pp. 1–4 doi:10.1093/rpd/ncp094

Radiation Protection Dosimetry Advance Access published May 25, 2009

district)(3): mainly consists of chalk, chert, marl andsome phosphate rocks. It outcrops mainly in theEastern Slopes of the district. Usually, the chalk iswhite but in some areas it takes the dark colour thatis due to the presence of bituminous materials.Whereas in Bethlehem formation(3), the northeasternpart of the formation is dominated by dolomite anddolomitic limestone, whereas the southwestern partis particularly chalky. Hebron formation(3): the baseof the formation consists of dolomite and dolomiticlimestone whereas the top consists of dolomitic lime-stone. Southern parts of Hebron are mainly com-posed of chalk, limestone and marl with a fairlythick soil cover. Most of the locations of in situmeasurements are characterised by a soil cover ofsandy nature. The average rainfall in these areasdoes not exceed 200 mm per year.

MATERIALS AND METHODS

The detector used in this work is a scintillation of76.2 � 76.2 mm NaI (Tl) crystal with a resolution of7.5% at 662 keV from 137Cs. Detector is connectedto Inspector 2000 multichannel analyzer and laptopcomputer. Collected spectra are analysed usingGenie 2000 Basic spectroscopy software. This soft-ware provides independent support for multipledetectors, extensive networking capabilities, window-ing interactive human interface and comprehensivebatch procedure capabilities.

Energy calibration is performed using a Petri dishmultigamma standard containing radionuclides of

energies that cover the energy range from 60 keV to3 MeV.

Efficiency calibration was performed theoreticallyusing Monte Carlo calculations, assuming a soildensity of 1.3 g cm23 (this value is the averagemeasured soil density in the study area) and homoge-neously distributed activity of the radionuclides ofinterest within a circle of 20 m in radius and in the top15 cm of the soil. This area represents approximately98% of the activity of radionuclides detected by thedetector placed 1 m above the ground surface(4).

Monte Carlo calculations are performed in twosteps: first, photons of the energies 609.3, 911.6 and1460 keV are randomly generated in a layer of soil atvarious depths; in the following step, the history andtransport of each photon is followed until it interactswith the crystal or escapes from it. Detector responseis then calculated from the energy of photons depos-ited in the NaI (Tl) crystal. Background spectrum ismeasured at every location using the upward detectorgeometry at 1 m height above the ground level with asheet of lead placed on the ground surface below thedetector. Each spectrum is collected for at least 1 h.All measurements were conducted in summer time,where the soil was very dry and therefore, soil humid-ity does not play an important role in affecting themeasured gamma-ray spectra.

Sensitivity of the detection system

The sensitivity of the detection system is estimatedby calculating the minimum detectable amount(MDA) of radionuclides of interest using the follow-ing equation(5):

MDA¼q2þ2q½ðN2nÞð1þN

2nÞðP

BiþP

BjÞþIþs2i �

1=2

TeYm;

ð1Þ

where q is the quantile of normal distribution (forconfidence level of 68.27%, q is 0.5); e, the detectorefficiency; Y, the yield; T, the time of measurement;N, the number of channels in the peak of interest; n,the number of background channels on both sides ofthe peak of interest; Bi, the sum of counts in the ithchannel; Bj, the sum of counts in the jth channel; I,the net peak area; s, the error of determination ofarea I and m, the mass of soil layer ‘seen’ by thedetector.

Figure 2 illustrates the method used for MDAdetermination.

Total absorbed dose rate D, in nGy h21 is calcu-lated using the following equation:

D ¼ 0:042 Ak þ 0:429 Au þ 0:666 ATh; ð2Þ

Figure 1. Locations of in situ measurements.

A. LAHHAM ET AL.

Page 2 of 4

where Ak, Au and ATh are the activity concentrationsof 40K, 238U and 232Th in Bq kg21, respectively.This study shows that variation in concentrations ofmeasured radionuclides over the whole study area islarge. Therefore, mean activity concentrations aswell as gamma dose rate are calculated for eachregion separately.

RESULTS AND DISCUSSION

Results are summarised in Figures 3 and 4 and inTable 1. Figure 3 shows a background spectrum col-lected using detector positioned 1 m above theground level with a sheet of lead positioned onthe Earth’s surface below the detector to reduce theeffect of photons reaching the detector from theground.

137Cs is identified only in four locations.Measured gamma-ray spectra at these locations indi-cate that the amount of this radionuclide is toosmall to be quantitatively analysed by the useddetection system. This radionuclide is present inPalestine due to global atmospheric releases. Its pres-ence after Chernobyl accident has been reported insome studies in Syria, Jordan, Saudi Arabia andIsrael. Figure 4 illustrates a gamma-ray spectrummeasured in situ in Beit Sahour town nearBethlehem. The spectrum indicates the presence of137Cs in this area. Results of activity concentrationsand dose rate calculations are presented in Table 1.

The lowest outdoor gamma dose rate due to theinvestigated radionuclides over the whole study areais 6 nGy h21 being in Tarqumia town, near Hebroncity. This location is characterised by very lowactivity concentrations of the three primordial radio-nuclides. The geology of this area consists mainly oflimestone. The highest gamma dose rate(30 nGy h21) is found in Abu Dies at Al-QudsUniversity Campus. This highest value (in compari-son to others in this study) is attributed to the exist-ence of some phosphate rocks in Abu Diesformation. The average gamma dose rate due to

40K, 238U and 232Th is 18+7 nGy h21. This valuerepresents only about 30% of the world average of0.059 mGy h21 of the terrestrial outdoor gammadose rate according to UNSCEAR 2000(9).

Generally, all the investigated locations show rela-tively low activity concentrations of potassium,uranium and thorium. Limestones are characterisedby their poor content of these elements. Relatively,the highest concentrations of Th and U are found inAbu Dies formation, which mainly consists of chalk,chert, marl and some phosphate rocks. The existenceof phosphate rocks explains mainly the higher con-centrations of uranium in comparison with the othertwo formations.

The sensitivity of the detection system is estimatedby calculating the MDA of 40K using equation (1),for 1 h measuring time and confidence level 68.27%and is found to be around 1 Bq kg21.

CONCLUSION

The importance of this study stems from the follow-ing: first; it is the first attempt to study radioactivebackground in Palestine; and it has establisheda good basis for environmental radioactivity

Figure 4. Part of in situ measured gamma-ray spectrumshowing the identified 137Cs in Bethlehem area.

Figure 2. Method of MDA determination for 40K. Figure 3. Background spectrum measured using upwarddetector geometry at 1 m height above the ground level at

Al-Quds University site.

ENVIRONMENTAL RADIOACTIVIY IN PALESTINE

Page 3 of 4

investigation. The system used for measurementsprovided good performance in terms of qualitativestudy of gamma-ray spectra emitted from the earthcrust. Even though, the resolution of the scintillationdetectors is a disadvantage in comparison with high-resolution germanium spectrometers, these detectorscould provide convenient results (if high-purity ger-manium detectors are not available), if the scintil-lation spectrometers are well calibrated and if anappropriate software for spectra analysis is used.This study has shown that levels of naturally occur-ring gamma-emitting radionuclides and therefore theresulted total gamma dose rate in the study area arerelatively low.

ACKNOWLEDGEMENT

The authors would like to thank Mr MohammadSbeih for his helpful cooperation in preparing themap of measurement locations.

REFERENCES

1. United Nations. Ionizing radiation: sources and biologi-cal effects. United Nations Scientific Committee on theEffects of Atomic Radiation, 1982. Report to theGeneral Assembly, with annexes (New York: UN)(1982).

2. Guy, S. An overview of natural background radiationsources. Part 1: External sources of radiation exposure(USA: Alara Consultants cc) (1988).

3. Applied Research Institute—Jerusalem (ARIJ).Environmental Profile for the West Bank: Bethlehem,Hebron, and Jerusalem Districts. Report by Jad Isaac,Vols 1, 3 and 6 respectively (ARIJ Publications) (1995).

4. International Atomic Energy Agency. Guidelines forradioelement mapping using gamma ray spectrometrydata. IAEA-TECDOC-1363 (Vienna: IAEA) (2003).

5. Bucina, I. and Malatova, I. Some remarks on statisticalmeasures of lower limit of detection. In: Proceedings ofthe Third International Conference on Low LevelCounting, Low Radioactivity 85 (Bratislava,Czechoslovakia: University Comeniana) (1985).

6. International Atomic Energy Agency. Construction anduse of calibration facilities for radiometric field equipment.Technical Reports Series No. 309 (Vienna: IAEA) (1989).

7. Michalis Tzorzis and Haralabos Tsertos. Determinationof thorium, uranium and potassium elemental concen-trations in surface soils in Cyprus. J. Environ. Radioact.77, 325–338 (2004).

8. Malczewski, D., Teper, L. and Dorda, J. Assessment ofnatural and anthropogenic radioactivity levels in rocksand soils in the environs of Swieradov Zdroj in Sudetes,Poland, by in situ gamma-ray spectrometry. J. Environ.Radioact. 73, 233–245 (2004).

9. UNSCEAR. United Nations Scientific Committee on theEffects of Atomic Radiation. Report of UNSCEAR to theUN General Assembly (New York: UNSCEAR) (2000).

Table 1. Activity concentrations of 40K, 238U and 232Th and calculated outdoor absorbed dose rate in the measured locations.

Location Activity concentration (Bq kg21) Total dose rate (nGy h21)

40K 238U 232Th

Jerusalem 1 99 17 15 212 89 14 19 223 67 15 20 224 55 17 9 165 51 19 30 306 49 32 12 247 68 31 19 29Mean 68+19 21+8 18+7 24+5

Bethlehem 8 201 13 8 199 127 19 6 1710 203 21 14 2711 88 9 11 1512 197 22 10 24Mean 163 +53 17+6 10+3 20+5

Hebron 13 13 7 5 1014 8 16 5 1115 13 16 6 1216 12 16 7 817 10 11 5 618 10 6 5 9Mean 11+2 12+5 6+1 10+2

Numbers 1–18 correspond to locations shown in Figure 1.

A. LAHHAM ET AL.

Page 4 of 4